Simple
Because, speaking of execution plan, the value can't be known at
compile time.
It can be '%something%' at runtime, so index optimization is not
possible.


--- In firebird-support@yahoogroups.com, "zdeseb" <Zdenek.Sebl@m...>
wrote:

> Thanks, it solved my problem.
>
> But I don't understand why otimizer switch off index optimization. Is
> there any VARCHAR value for which is optimal to DO NOT USE index in
> this situation?
>
> Zdenek
>
> --- In firebird-support@yahoogroups.com, "Dorin Vasilescu"